Directions

Make the Onion Filling: Heat oven to 350 degrees F. Bring a large saucepan of water and 1 tablespoon of salt to a boil. Add the onions and cook for 2 minutes. Remove from the pan and roughly chop into 2-inch pieces.

Tightly cover the pan with aluminum foil, roast for 15 minutes, remove the foil, and continue to roast until onions are tender and lightly caramelized, about 45 minutes. Remove the onions from the pan and let cool slightly.

Assemble the tart: Combine the Manchego cheese, cream cheese, remaining salt, and the garlic and lemon zest. Carefully spread the cheese mixture onto the bottom of the tart shell and top with the onions. Remove the tart from the pan and serve.